CAPE CANAVERAL, Fla. — NASA decided Thursday that no repairs are needed for a deep gouge in Endeavour’s belly and the space shuttle is safe to fly home.

Mission Control notified the seven shuttle astronauts of the decision right before they went to sleep, putting an end to a week of engineering analyses and anxious uncertainty — both in orbit and on Earth.

Endeavour’s relieved commander, Scott Kelly, thanked everyone on the ground for their hard work. Mission Control replied, “It’s great we finally have a decision and we can press forward.”

Mission managers received the results of one final thermal test on Thursday, then spent five hours debating whether or not to go ahead with potentially risky spacewalk repairs.

Their worry was not that Endeavour might be destroyed and its seven astronauts killed in a replay of the Columbia disaster — the gouge is too small to be catastrophic. They were concerned that the heat of re-entry could weaken the shuttle’s aluminum frame at the damaged spot and result in lengthy postflight repairs.

Decision not unanimous
The massive amount of data from NASA’s analyses indicated Endeavour would suffer no serious structural damage during next week’s re-entry. But Thursday night’s decision was not unanimous. The chairman of the mission management team, John Shannon, said Johnson Space Center’s engineering group in Houston wanted to proceed with the repairs. He quoted the group as saying, “We're OK with ‘use as is,’ but ... we think it would be prudent to repair.”

“I am 100 percent comfortable that the work that has been done has accurately characterized it (the damage) and that we will have a very successful re-entry,” Shannon said. “I am also 100 percent confident that if we would have gotten a different answer and found out that this was something that was going to endanger the lives of the crew, that we had the capability on board to go and repair it and then have a successful entry.”

The astronauts had spent much of the day running through the never-before-attempted repair methods, just in case they were ordered up.

Endeavour’s bottom thermal shielding was pierced by a piece of debris that broke off the external fuel tank shortly after liftoff last week. The debris, either foam insulation, ice or a combination of both, weighed just one-third of an ounce (10 grams) but packed enough punch to carve out a 3.5-inch-long, 2-inch-wide (9-by-5-centimeter) gouge and dig all the way through the thermal tiles. Left completely exposed was a narrow 1-inch (2.5-centimeter) strip of the overlying felt fabric, the last barrier before the shuttle’s aluminum structure.

The only way to fix the gouge would have been to send a pair of spacewalking astronauts out with black paint and caulklike goo, and maneuver them beneath the shuttle on the end of a 100-foot (30-meter) robotic arm and extension boom, with few if any close-up camera views of the work.

Risk factors
The spacewalk, which was slated for Saturday, would have involved many untried procedures, and it ran the risk of doing further damage to the shuttle. That's why mission managers didn't want to attempt the operation if it was unnecessary. Wednesday’s spacewalk, cut short by an astronaut's ripped glove, showed how hazardous even a relatively routine spacewalk can be.

Putting goo into the gouge would have introduced an extra level of uncertainty, Shannon said. “Once we do the spacewalk and put material in the bottom of the cavity, we have a new cavity that we have not analyzed,” he said. NASA plans to test the goo on a future shuttle flight in order to have more confidence in case it’s ever needed for real, Shannon said.

There will still be a spacewalk on Saturday, but Canadian astronaut Dave Williams and space station crew member Clay Anderson will be taking on less risky installation tasks.

Before the decision was announced, astronaut Alvin Drew said from Endeavour that he was comfortable with the prospect of flying back to Earth in a gouged ship. Engineers seem confident, he said, “and I trust their confidence that we can get home safely even with the divot that we have in the belly.”

“Spaceflight is risky,” noted astronaut Barbara Morgan, the backup teacher for Challenger’s doomed mission, “but we have all confidence that we’re going to be able to do the right thing.”

Not everyone was convinced NASA's decision was the right one. Stanford University's Douglas Osheroff, a Nobel Prize-winning physicist who served on the Columbia investigation board four years ago, questioned NASA’s hesitancy to perform the repairs since they “can only increase their chances of making it down.”

“I don’t see why NASA is going to invent a fix and not use it,” Osheroff said. He added: “This attitude of, ‘It looks like it’s OK, let’s not do anything about it,’ it seems like the Columbia NASA.”

Another lesson in space
In a poignant reminder of NASA’s other shuttle accident, the 1986 Challenger launch explosion, Morgan — Christa McAuliffe’s backup — answered questions from youngsters gathered at the Challenger Center for Space Science Education in Alexandria, Va.

The moderator was June Scobee Rodgers, the widow of Challenger’s commander and the founding chairman of the Challenger center’s board. “Barb, we have been standing by waiting for your signal from space for 21 years,” she said.

“Some of my mentors that have meant more than anything to me are seven very special people who I believe are mentors to you, too, and that was the Challenger crew,” Morgan replied. She closed the teaching session by holding up an emblem of the Challenger crew’s mission patch.

Later in the day, Morgan talked via ham radio with students at the Idaho elementary school were she taught before moving to Houston in 1998 to become the first teacher to train as a full-fledged astronaut. The radio operator wasn’t able to get through the first time, but made contact on the second attempt.

Replying to the students' questions, Morgan described how much G-forces increase during launch ("It kind of feels like somebody's standing on your chest") ... how fun it is to eat in zero-gravity ("You can even play with your food") ... and how easy it is to sleep in space ("Once I shut my eyes, I go to sleep right away").

She also faced a question she has encountered repeatedly during her years of training: Would she rather be a teacher or an astronaut?

"Do I have to choose one, or can I do both, please?" Morgan replied. "They’re both wonderful jobs, I highly recommend both."

Morgan conducted her
first Q&A
with students on Tuesday, and is scheduled to do one more session with a school in Massachusetts on Sunday. She told the Idaho students that she would be telling them much more about her trip after her return to Earth. "I miss you," she said.

This report includes information from The Associated Press and MSNBC.com.

The 12 orbiting astronauts on the International Space Station were hailed by the chief on Thursday — and also got a humorous scolding for keeping their android crewmate locked up in its packing for so long.